1. Field of the Invention
The present invention relates to an adjustment device, and more particularly to an adjustment device composed of two worm gears coaxially combined together, two worm wheels respectively engaged with the two worm gears, and a shaft with a locking device.
2. Description of Related Art
A wire-guiding adjustment device is a structure for winding and releasing wires to vary positioning of an attached element by controlling the released length of the wires. For example, if an upper end and a lower end of a resilient backrest are controlled by the wires, the resilient backrest is bent into a big curved arc when the wires are wound to be shorter. On the other hand, when the wires are released to be longer, the resilient backrest rebounds to a straight shape. Therefore, the wire-guiding adjustment device has a wide application and various modifications in structures.
A conventional wire-guiding adjustment device is limited in technical aspects and generally comprises a single guiding wheel that can be selectively arranged to receive one or two counter wound wires to synchronously operate the wires for changing the shape or position of the attached element such as the resilient backrest. However, controlling the resilient backrest usually needs multiple sets of the wire-guiding adjustment devices. For example, two conventional wire-guiding adjustment devices are needed for arc control and height control of the resilient backrest in operation. Providing the resilient backrest with the wire-guiding adjustment devices is not only cost-wasting but also time-consuming, because it is hard to find proper locations and spaces for multiple sets which are neat in appearance and also not confusing in functions to users.